Active Elastic Materials : from emerging collective motion to autonomous actuation*

A population of motile units does not only display collective motion at all scale; it can also generate active forces when embedded in an elastic matrix. A typical biological instance of such processes is that of migrating cells that transmit forces to the extracellular matrix via actin filament contractions. Mimicking such processes is a natural path towards the design of autonomous functional materials. With the help of centimetric model of self-propelled particles, we construct the first experimental model system of an active elastic material, and study its emerging behaviors in various mechanical conditions. We find that self-propelled particles acting at the nodes of an elastic structure spontaneously organize and actuate a variety of mechanical functions, including rigid body motion, mechanisms actuation and selected excitation of vibrational mode. Such active solids present very peculiar dynamical behaviors in strong violation of the equilibrium principles, and open the way toward the autonomous actuation of more advanced synthetic networks, including shape-morphing, topological and nonlinear meta materials, with predesigned functionality.